'Black Sheep" is a little comedy that succeeds in its modest aim to provide 87 minutes of harmless diversion. If you have nothing to do -- and I mean absolutely nothing -- "Black Sheep," which opens today, is a must-see.

The picture stars Chris Farley and David Spade, a pair of comic actors who had a hit last year with "Tommy Boy." "Black Sheep" rehashes the "Tommy Boy" formula, recasting Farley as a family misfit and Spade as his caretaker.

What's interesting about "Black Sheep" is its sledgehammer approach to comedy, which, in comparison, makes "Tommy Boy" look like a Noel Coward work. The picture begins with Farley, as Mike, accidentally wrecking a campaign rally for his gubernatorial candidate brother (Tim Matheson) with a truck.

KEEPING AN EYE ON MIKE

When a campaign worker (Spade) is assigned to keep Mike under wraps, the two go off to a cabin in rural Washington state, which provides the setting for a series of slapstick gags. Most of these bits come out of nowhere -- with little or no relationship to anything that happens before or after. Watching "Black Sheep" is a little like watching "Roadrunner" cartoons.

The fellows wrestle with a bat in the cabin. . . . Kids drive by and squirt Spade with a fire extinguisher. . . . Farley falls all the way down a mountain . . . A huge boulder destroys the cabin. . . . The roof blows off. . . . It starts hailing. . . . Then the top bunk collapses under Farley's weight and lands on Spade. All within 15 minutes.

Farley and Spade are funny, and they're funny together. And after a while, sheer relentlessness and predictability make the movie funny, too. Farley goes to vote -- and annihilates the voting booth. Surprise, surprise.

BEST WHEN GROUNDED IN POLITICS

But "Black Sheep," which was directed by Penelope Spheeris ("Wayne's World"), is at its best when the comic business is grounded in the political story. In one scene the straitlaced brother is about to address an MTV rock-the-vote concert. Instead, black-sheep Mike, stoned, is pushed on stage and is mistaken for the candidate.

Farley is at his best in the concert scene. Buoyed by the cheering, he says anything, carrying on like an idiot-slob. He is the nightmare brother for a serious politician. Or as someone puts it, "He's Billy Carter, Roger Clinton and Ronald Reagan's whole family rolled into one."

Spade has no similar opportunity to shine here. In "Tommy Boy" he got to be snide and officious, but here he's mostly a straight man, and it's a waste of a good comedian. If Farley and Spade are to continue making movies together -- and they should -- they're going to need scripts that play to both their strengths.

Gary Busey also makes an appearance in "Black Sheep," but in the relatively small role of a survivalist. Busey is onscreen just long enough to smile and make you wonder how he fits all those teeth in his mouth.